Tornado Tube

thingiverse

I found that a few of the other designs were difficult to hold onto while wet, so adjusting if there was a spill became a pain. I designed mine with some grip and a center funnel down to 15mm that doesn't require supports on a decently tuned printer. The threads are solid but not perfect, nor is the seal against the funnel, but 2 wraps of teflon tape hasn't leaked in a week of daily use by my son. I have also found that using a standard set of pliers on the extended setting to grab the neck of the bottle helped get a snug fit, but it's 3D printed, so just snug or you might crack it.